The present invention relates to a screw-thread arrangement, and to a conversion arrangement for mounting optical units on cameras, particularly though not exclusively on film or television cameras.
Accordingly, the present invention provides a screw-thread arrangement for enabling two coaxial members to be rotated relative to one another to move the members axially one relative to another, the arrangement comprising:
a screw-thread formed on a radial surface of a first of the members and radially spaced from a second of the members; a plurality of follower positioned between the co-axial members and supported on the second of the members;
and means biasing the followers into engagement with the screwthread to cause the followers to follow the screw-thread on relative rotation of the members to move the members axially relative to one another.